1. Field of the Invention
This invention relates generally to the art of leg prosthesis and, more particularly, to a prosthetic knee joint having a four-bar linkage system.
2. Description of the Prior Art
As is well known in the art, several problems and difficulties are encountered in providing a desirable artificial knee joint that is capable of geniculating in a manner similar to the human knee.
Considerable study and effort have been directed to improvement in leg prosthesis, especially as it relates to knee joints in artificial legs for the severely handicapped amputees.
The knee joint in a standard artificial limb is traditionally of the single-axis type which, in the past, has provided an acceptable function for many amputees. In this design, knee stability during weight-bearing is achieved by positioning the knee axis in such a way, relative to the body-weight action line, that the knee can be extended. In addition, a movement from active hip-extension muscles is required during the weight-bearing phase of the walking cycle. This means that the amputee must walk during weight-bearing over a fully extended knee, which is physiologically abnormal and contributes to the unnatural appearing gait of the "above-knee" amputees. Furthermore, when amputations are performed through the knee joint, the resulting long stump leaves insufficient space for the single-axis knee mechanism. In this case, single-axis side joints are required, resulting in greater fabrication time and an unpleasant appearance of the finished device due to excessive width of the knee.
These and other shortcomings of the single-axis design have encouraged those knowledgeable in the art to seek other mechanisms for knee devices.
Thus, the applicant herein discloses a four-bar linkage system, which yields polycentric (or many centered) action of the center of knee rotation.